Upgrading natural gasoline



Sates Unite The present invention relates to the upgrading of naturalgasoline and is particularly concerned with improvements in process forthe production from such liquid condensates of natural gas, of desirablyhigh -yields of liquid products having octane ratings of 90 or more (F-lclear), for use as a component of motor ga'soline,'particularlyingasoline pools for present-day superfuels having octane ratings of 100or more (F-l clear).

Of the numerous grades of natural gasoline known and marketed, theaccepted grades have the common characteristic of being highlyparaflinic and composed principally of hydrocarbon components in thelower boiling end of the gasoline range such that not less than 90% ofthe natural gasoline evaporates at 275 F. and the end point of the totalgasoline is no higher than about 375 With increasing demands forgasolines of higher and higher anti-knock ratings for use as motor fuelin the newer high compression internal combustion engines, the positionof natural gasoline in the motor fuel market has weakened considerably.The usual methods for upgrading of virgin naphthas, such as byhydrogenative reforming over noble metal catalyst, have not been founddesirable for the needed upgrading of natural gasoline. Numerousprocessing schemes have been studied with the view of improving orpreserving the position ofthe natural gasoline producer in themotor fuelmarket. Of these, the processes most widely advocated involveisomerization of the C and C fractions of the natural gasoline employingeither noble metal catalyst or aluminum chloride type catalysts. Theseadvocated processes have not been successful, however, in achievingdesired high octane levels at acceptable yields, since the octaneceilings obtained at equilibrium isomerization fall short of the valuesdemanded to permit blending of these products in the present higheroctane motor fuels, and separation of the obtained isomers of desirablyhigh octane quality is difiicult to achieve and uneconomic.

In accordance with the present-invention products of desirably highoctane quality are obtained from natural gasoline by a combination ofprocess steps involving fractionation of such gasoline to provide'alower boiling cut composed chiefly of C and C hydrocarbons (boiling inthe range of up to about 160-185, F.) and a residual cut comprising thehigher boiling portion of the natural gasoline composed of 90-95% ormore or C7 and C hydrocarbons with a small amount of higher boilinghydrocarbons. The lower boiling fraction is subjected to catalyticdehydrogenation and the higher boiling fraction to hydrogenativecatalytic reforming; the products of these steps being blended toprovide an improved natural gasoline product having an octane clearrating of at least 90 (F-l).

A debutanized natural gasoline having a 67 F-l clear octane rating isupgraded by the process of the invention to a 93 F-l clear product at aliquid yield level of 83 volume percent, The yields and the octanesobtained by this combination of steps are superior to that obtainableby:

A. Dehydrogenation of the total natural gasoline, which is limited toF-l clear octane values not in excess of about 88; B. Hydrogenativereforming of the total natural gasoline ammo Patented Jan. 9, 1962 icewhich produced only a 72 volume percent yield at the '88 F-l clearoctane level; or

C. Dehydrogenation of the 0;, fraction only, with catalyt-ic reformingof the C -C fraction, by which a 93 F-l gasoline product could beobtained but with significantly lower yields of liquid than thatobtainable at the combination under A above.

On the other hand, while at lower octane levels desirably high yields ofC and C fractions can be obtained by isomerization, this route islimited in that the octane ceiling obtainable by vapor phaseisomerization of pentanesv (at SOD-950 F.) lies at about 84 F-l clearand that obtained from vapor phase isomerization of hexanes is not inexcess of 76 F-l clean Isomerization of all or part of a debutanizednatural gasoline, accordingly, cannot be employed to obtain upgradedproducts in excess of 90 F-l clear at the required high yieldscomprising 85% or more by volume of the charge. The problem is furthercomplicated in that possible or suggested procedures involvingfractionation of the equilibrium isomerizate and recycling of the normalpentanes and/or hexanes to further isomerization sufier from thedrawback that such separation is difficult and expensive.

In the accompanying drawing there is shown a schematic flow diagramillustrating the practice of the invention.

In the practice of the present invention dehydrogenation of the C -Cfraction is carried out preferably over chromia-alumina catalyst attemperatures in the range of 900-l050 F. at about atmospheric pressureand at a liquid hourly space velocity of about 1-4. If desired,

hydrogen or hydrogen-rich gas may be added or recycled to the reactorcharge; it has been found beneficial, particularly when thedehydrogenation is effected at high conversion levels.

The reforming of the 07+ hydrocarbon fraction of natural gasoline ispreferably carried out over supported platinum catalyst, typically overcatalyst preparedv by impregnation of porous alumina with chloroplatinicacid, wherein such reforming is effected at temperatures in the range ofabout 800-1000 F., at pressures of about 200- 600 p.s.i.g., and atliquid hourly space velocities of about 1-5, hydrogen-rich gas beingrecycled to the reactor in amounts providing a hydrogen to oil ratio ofabout 3 or more. The activity of the catalyst can be maintained, wherenecessary, at desired high levels for longer operating periods by theinclusion of a small amount of halide compound in the feed correspondingto about 50 ppm. of t-butyl chloride by weight of liquid charge, I

Example I Out Cr .Cu C -C Total 1 to 260 Boiling Range, F--." 75115 -185-btms. (95% pt.)

- 310 dry point Vol. percent of Gasoline 42. 8 28. 6 28. 6 Octane No.(F-l Clear) 75. 9 67. 5 66. 4 67. 1

Paraffins, vol. percent 98. 3 71. 5 42. 6 74. 7 Olefins, vol. percent 1.7 0 O. 9 1.0 Naphthenes, vol.

percent 0 26. 7 50. 7 22. 1 Aromatics, vol.

percent 0 1. 8 5.8 2. 2

(a) By separate dehydrogenation of the C cut over catalyst containing20% Cr O on activated alumina, at 1000 F. (outlet temperature)atmospheric pressure and at a liquid hourly space velocity of 1 volumehydrocarbon per volume of catalyst, one mol hydrogen being added withthe charge, there is obtained a product having an average octane (F-lclear) of 93 at yields of 89-90 volume percent of charge.

(b) The C cut was separately dehydrogenated over the same chrome-aluminacatalyst above described .at 1000 F. (average), 1 atmosphere, and at. aliquid hourly space rate of 1 with the addition of 1 mol of hydrogen permol of hydrocarbon charged. The dehydrogenated product obtained at 92volume percent C yield had an F-.1 clear) octane rating of 82..

(c) In a typical operation, dehydrogenation of the above-combined C Cfractions as found in the described natural gasoline, operating at 1000F., 1 space rate (v./hr./v.) and atmospheric pressure with 1 mol Example[I The 0,-1- cut of the natural gasoline described in the previousexample was reformed over catalyst composed of 0.5% Pt on activatedalumina (prepared by impregnation of the alumina with cliloroplatinic,acid and subsequent hydrogen reduction) at 950 F.,' 300 p.s.i.g., and ata volume space rate of 3 .(v./hr./v.). There was obtained 74% by volumeof C;,-{ gasoline having an octane rating of 103 F-l (clear).

By combining the reformate With the C -C dehydrogenation efiluentobtained according to Example Ic above, there was provided an upgradedgasoline of 92 F-1 clear octane rating at a yield of 86% by volume ofthe original C natural gasoline.

Compared with the results obtained above, by reforming the total naturalgasoline (C to bottoms) there is obtained at the 80% yield level an 83octane product, or with increased severity of operation a 72% yield ofliquid product at the 88 octane level.

The C to bottoms fraction can be reformed to 103 F'-l clearoctane levelover platinum catalyst without necessitating frequent regeneration. Theoctane value of the blend of this reformate with the dehydrogenated C5-Cfraction will depend upon severity of the dehydrogenation whichdetermines the octane value to which the latter fraction is brought.Thus, by bringing the C -C fraction to 72 (F-l clear) octane andblending with the reformate, the blend will have 79 octane; for a 90F-1clear blended gasoline the C -C fraction must be brought to 85.9 octanelevel. In most instances no significant advantage is obtained forseparate dehydrogenation of the C and C cuts, respectively; separatedehydrogenation of the'C and C cuts may be practiced, if desired, withsome benefit, by choice of optimum conditions for each of these cuts,particularly in those instances in which each of the cuts is high innormal parafiin content. For separate dehydrogenation the C cut isprocessed at 950-1050 F.'while the 0, out can be treated at lowertemperature and/or higher space rate.

gen'ated product with the reformed C cut, the operator can select theseverity of the dehydrogenation operation for optimum yield-octanevalues.

The advantages of the process of the invention are not limited totreatment of natural gasoline, but can be beneficially applied with C -Chydrocarbon fractions from other sources. With any type of charge stock,such as that employed in the illustrative example, wherein the C cut ishigh in paratfins, the inclusion of the C cut in the charge to reformingis not desirable. As a criterion in the choice of the manner of handlingthe several cuts contained in a C -C gasoline fraction, it is suggestedthat for those cuts wherein the paraiiin/naphthene weight ratio is equalto 2 or more, dehydrogenation is the best route; for those cuts in whichthe paraffin/naphthene weight ratio is 1 or less, reforming isindicated. Where the paraflin/naphthene ratio lies between 1 and 2, theoperator has the choice of reforming if high octane number is preferredF-l clear) or dehydrogenation if highest yields 90%) at moderate octaneare desired.

Obviously, many modifications and variations of the invention as.hereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims. I

What is claimed is:.

1. The method of upgrading natural gasoline which comprisesfractionating such, gasoline at a cut point in the range of l 6018 5 F.to provide (1) a major fraction of lower boiling hydrocarbons composedchiefly of C and C hydrocarbons and (2) a minor fraction of higherboiling hydrocarbons of which at least 90% by volume is composed of Cand C hydrocarbons, passing said lower boiling fraction at catalyticdehydrogenation conditions including substantially atmospheric pressureover chromium oxide-alumina dehydrogenation catalyst and at a processingseverity level to obtain therefrom a liquid condensate of at least 85.9octane level (F clear), collecting the condensable eflluent from saiddehydrogenation; subjecting the higher boiling fraction to hydrogenativereforming over supported platinum catalyst at a temperature in the rangeof 800-1000" F. and at a pressure of 200 to 600 p.s .i.g., and blendingthe liquid condensate from said hydrogenative reforming with thecondensable effiuent from said dehydrogenation to provide an upgradedgasoline material having an octane number of at least 90 (E clear).

2. The method in accordance with claim 1 wherein said fractionation ofthe natural gasoline charge is made at a cut point within the definedrange such that the higher boiling fraction predominates in naphthenes.

References Cited in the file of this patent UNITED STATES PATENTS2,304,183 Laynglet al. Dec. 8, 1942 2, 24,16 Layne e a1. July 13, 19432,348,599 Brown May 9, 1944 2,689,208 Murray et al. Sept. 14, 19542,767,124 Myers Oct. 16,1956 ,3 14 R d l1j 1 2,905,619 Sutherland Sept.22, 1959 2,918,422 Evering et al. Dec. 22', 1959,

1. THE METHOD OF UPGRADING NATURAL GASOLINE WHICH COMPRISESFRACTIONATING SUCH GASOLINE AT A CUT POINT IN THE RANGE OF 60-185*F. TOPROVIDE (1) A MAJOR FRACTION OF A LOWER BOILING HYDROCARBONS COMPOSEDCHIEFLY OF C5 AND C5 HYDROCARBONS AND (2) A MINOR FRACTION OF HIGHERBOILING HYDROCARBONS OF WHICH AT LEAST 90% BY VOLUME IS COMPOSED OF C7AND C5 HYDROCARBONS PASSING SAID LOWER BOILING FRACTION AT CATALYTICDEHYDROGENATION CONDITIONS INCLUDING SUBSTANTIALLY ATMOSPHERIC PRESSUREOVER CHROMIUM OXIDE-ALUMINA DEHYDROGENATION CATALYST AND AT A PROCESSINGSEVERITY LEVEL TO OBTAIN THEREFROM A LIQUID CONDENSATE OF AT LEAST 85.9OCTANE LEVEL (F1 CLEAR), COLLECTING THE CONDENSABLE EFFLUENT FROM SAIDDEHYDROGENATION; SUBJECTING THE HIGHER BOILING FRACTION TO HYDROGENATIVEREFORMING OVER SUPPORTED PLATINUM CATALYST AT A TEMPERATUARE IN THERANGE OF 800-1000*F. AND AT A PRESSURE OF 200 TO 600 P.S.I.G., ANDBLENDING THE LIQUID CONDENSATE FROM SAID HYDROGENATIVE REFORMING WITHTHE CONDENSABLE EFFLUENT FROM SAID DEHYDROGENATION TO PROVIDE ANUNGRADED GASOLINE MATERIAL HAVING AN OCTANE NUMBER OF AT LEAST 90 (F1CLEAR).